$ { \left[\begin{array}{rr}{-1} & {0} \\ {0} & {2}\end{array}\right]-\left[\begin{array}{rr}{1} & {4} \\ {2} & {1}\end{array}\right] = {?} } $
To find the difference of two matrices, subtract the corresponding items between each matrix. ${\left[\begin{array}{rr}{-1}-{1} & {0}-{4} \\ {0}-{2} & {2}-{1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{-2} & {-4} \\ {-2} & {1}\end{array}\right]}$